Half backspace for dual pitch typewriter

ABSTRACT

A pair of stop surfaces carried by a dual pitch escapement rack selectively directly measure half space displacement of the escapement rack in accordance with its selected pitch setting. Motion for half space displacement is derived from a circumferentially symmetrical face cam couple that directly converts input rotary motion into output linear motion of the escapement rack.

United States Patent 1ibbons et a1. 1 1 July 8, 1975 54] HALF BACKSPACEFOR DUAL PITCH 3,578,132 5/1971 Cremasco et al. 197/91 3,713,524 1973Forrest et a1 197/84 R 75] Inventors: John Gilbert Gibbons; RaymondOTHER C TIONS Michael Mamwski, both of 113M Technical DisclosureBulletin, Half-Space De- Lxmgt-ofly vice for Standard Typewriter," I(.A.Lennon, Vol. 8 73] Assignee: International Business Machines June ICorporation, Armonk, IBM Technical Disclosure Bulletin, Self-PhasingBackspace Mechanism," J.O Schaefl'er, V01. 12 No. 12] F1I6CI2 NOV. 23,1973 12 y 970 p 2 92 !1] Appl. No.: 418,349

12] U.S. C1 197/91; 197/84 R 1] Int. CL. B41J 19/62 8] Field of Search197/16, 84 R, 84 A, 84 B, 197/91, 176

6] References Cited UNITED STATES PATENTS 183,056 5/1916 Wiley 197/91365,629 12/1936 Thompson 162,565 6/1939 Ritterholz 546,086 10/1967Cralle et a]. 346,087 10/1967 Colombo et a1. 366,215 1/1968 Hosey et a1.197/91 340,565 11/1970 Hanft et a1 197/176 547,245 12/1970 Okcuoglu eta1 197/84 R X IBM Customer Instruction Manual Form No. 24156- 16-1Reprinted February 1972, pages 136-142,

Primary Examiner-Ernest T. Wright, Jr. Attorney, Agent, or Firm-LaurenceR. Letson {5 7] ABSTRACT A pair of stop surfaces carried by a dual pitchescapement rack selectively directly measure half space displacement ofthe escapement rack in accordance with its selected pitch setting.Motion for half space displacement is derived from a circumferentiallysymmetrical face cam couple that directly converts input rotary motioninto output linear motion of the escapement rack.

1 Claim, 3 Drawing Figures HALF BACKSPACE FOR DUAL PITCH TYPEWRITERBACKGROUND OF THE INVENTION The IBM SELECTRIC II typewriter as describedin IBM Office Products Division Customer Engineering Service Manual FormNo. 24l-56l5-l as reprinted February 1972, includes an escapement rackhaving two sets of teeth by which typing according to either of twopitches can be accomplished. A half backspace control lever is providedto act through a series of bell cranks and levers to displace theescapement rack in the backspace direction by an amount equal toone-half the normal letter feed spacing. The distance measurement forthe backspace motion is accomplished by a pair of limit stops whichprovide a constant input motion to the rack driving bell crank. Aselective lost motion connection between the rack driving bell crank andthe escapement rack itself converts the fixed input motion into eitherof the two half-space output motions required.

Inasmuch as the present mechanism is relatively complex and difficult toadjust, we have devised and developed a relatively simple mechanism thatdirectly measures the rack motion required. Our mechanism also providesa smooth, sure feel to the control lever. The half backspace device ofour invention directly combines a V-shaped face cam, with aself-detenting pointed or V-shaped follower cam, both of which aremounted coaxially of the escapement rack to convert rotary motion from acontrol arm directly into linear motion of the escapement rack. The facecam and follower cam provide symmetrical camming surfaces with respectto the axis of rack motion to obtain a smooth predictable linearmovement of the escapement rack. A stop member that is also mounteddirectly on the escapement rack, moves through an adjustable clearanceinto contact with a stationary abutment to measure the half backspacedisplacement. The stop member has two different stop portions which arelongitudinally offset and angularly spaced from each other so as to beassociated with the operative positions of the two sets of teeth,thereby alternately measuring the different size half backspace requiredfor each pitch of the typewriter.

These and other objects, features and advantages of our invention willbe apparent to those skilled in the art from the following more specificdescriptions of a preferred illustrative embodiment of our invention,wherein reference is made to the accompanying drawing, of which:

FIG. 1 is a perspective view of a dual pitch typewriter having a halfbackspace mechanism constructed in accordance with our invention.

FIG. 2 is a fragmentary perspective view of the half backspace mechanismshowing the details of its construction.

FIG. 3 is an enlarged exploded view ofa camming arrangement constructedin accordance with a preferred embodiment of our invention.

FIG. 1 shows a typewriter like that described in the aforesaid ServiceManual, including a paper support platen 11 that cooperates withprinting mechanism including a type element 12 to define a printingpoint 13 therebetween. Type element 12 is mounted on a carrier 14 thatis displaceable laterally along platen ll to move the printing point 13along a writing line 15. As shown in FIG. 2, carrier 14 is laterallypositioned by letter feeding mechanism including a pawl 16 thereon thatengages an escapement rack 17. Pawl 16 is arrested by a tooth of eithera first series of teeth 18 on rack 17 that are spaced one-twelfth of aninch apart or alternatively, with a tooth of a second series of teeth 19that are spaced one-tenth of an inch apart.

Selection of which series of teeth 18 or 19 is positioned to beoperatively engaged by pawl 16 is accomplished by pitch selectioncontrol lever 20. Control lever 20 is supported at one end ofa sectorlink 21 that is pivoted on axis 21a and includes gear teeth 22 thatengage complimentary teeth 23 in arbor 24 that is fixed to theescapement rack 17 by set screw 25. A spring 26 is tensioned betweenextension 27 on arbor 24 and a tab 30 on bracket 31 that is supported bytypewriter frame 32. The spring 26 urges a stop arm 28 into either theposition shown, where it engages tab 30 or an alternate position whereit engages a stationary frame mounted stud 33. The mechanism thusfardescribed is substantially identical to that described in theaforementioned Service Manual.

The half backspace mechanism of our invention includes a stop member 40that is attached by set screw 41 to the escapement rack 17. Stop member40 in cludes two longitudinally offset, angularly displaced stopsurfaces 42 and 43 which are respectively associated with the series ofteeth 18 and 19.

Escapement rack 17 is slideably carried by a bore 34 in FIG. 3 inbracket 31 that guides rack movement along an axis 29 that is parallelto writing line 15.

A stud or abutment 35 carried by the frame mounted bracket 31 is spacedfrom selected leftward facing stop surface 42 by a distance 44 of onetwenty-fourth of an inch, corresponding to one-half a one-twelfth inchtooth spacing of the teeth 18. A half backspace thus is measured simplyby bringing the stop surface 42 into engagement with abutment 35.

To generate the required motion, a stationary cam member 45 is securedto bracket 31 by bolt 46 adjacent the rack 17. Cam member 45 includes aV-shaped ramp camming surface 47 facing leftwardly along the rack axis29. A cooperating cam member 50 is rotatably carried on rack 17 adjacentcam member 45 and includes a relatively narrow, tooth or V-shaped camfollower portion 51 for engaging the sides of V-shaped camming surface47. Both surface 47 ahd follower portion 51 extend symmetrically ondiametrically opposite sides of the rack axis 29 thereby providing apair of camming surface portions that balance the forces ap plied to cammember 50 and avoid undesired canting thereof. Cam member 50 abuts arbor24 to deliver longitudinal motion to the rack 17 in opposition to aspring 52. Spring 52 is trapped by a clip 53 onto the rack 17 and abutsan offset bracket 54 carried by the bracket 31. Spring 52 and arbor 24thus effectively connect cam member 50 with the rack 17 for longitudinalmovement therewith without interfering with rotary or transversemovement of cam member 50 therebetween. The tooth shaped follower 51 issufficiently narrow that it seeks the apex of V-shaped camming surface47 under the urging of spring 52 to define a stable normal longitudinalposition of rack 17 at the point of maximum penetration.

An extending arm 55 of the cam member 50 is connected through a clevislink 56 to control lever 57 having operator graspable handle 58 thereon.Pivot connection 59 between clevis link 56 and control arm 57 issufficiently loose to allow both pivoting and tilting action of theclevis link 56 which is required to accommodate both rotary and axialmotion of the cam member 50.

To displace the printing point 13 by a half backspace, the operatorgrasps control handle 58 and moves it in the direction of arrow 60toward the front of the typewriter 10. This motion lifts arm 55 of cammember 50 driving the pointed follower 51 thereof against the rampcamming surface 47 of stationary camming member 45. The resultantcamming action drives cam member 50 against arbor 24 drawing rack 17leftwardly in FIG. 2 until stop surface 42 engages abutment 35. Releaseof control handle 58 allows spring 52 to restore the parts to theiroriginal condition. When pitch selection control lever 20 is displacedto its alternate position, stop member 40 will present the alternatestop surface 43 into alignment with abutment 35. Stop surface 43 isoffset from stop surface 42 by one-one hundred twentieth of an inchwhich represents one-half the difference between ten and twelve pitchspacing. The half backspace operation is identical to that describedabove with the exception that stop member 40 moves a slightly greaterdistance before stop surface 43 is arrested by engagement with abutment35. In both cases, the operator feels a smooth consistent action at thecontrol handle 58 which is terminated by a clear stop. Set up adjustmentis accomplished simply by the use of a feeler guage for locating surface42 the proper dis tance 44 from abutment 35 prior to tightening setscrew 41.

Those skilled in the art will recognize that we have disclosed aparticularly simple and easy to adjust half backspace mechanismparticularly suited for a dual pitch typewriter. it will be furtherrecognized that various modifications. additions and deletions can bemade to the particular embodiment disclosed without departing from thespirit and scope of our invention as defined by the appended claims.

We claim:

1. A typewriter having printing and paper support means definingtherebetween a printing point movable along a writing line, frame means,letter feeding mechanism comprising an escapement rack, means supportingsaid escapement rack on said frame means for movement along an axis thatis parallel to said writing line, wherein the improvement comprises:

first and second opposed camming members,

connecting means connecting said first camming member to said escapementrack for unitary move ment therewith in a first direction that isparallel to said writing line,

means connected with said frame means for support ing said secondcamming member against movement in said first direction,

one of said camming members being supported for movement relative to theother said camming member in a second direction that is transverse tosaid first direction,

said first and second camming members each providing a plurality ofcamming surface portions that are symmetrically spaced about said axisof rack movement and are mutually configured such that rela tivemovement therebetween in said second direction produces relativemovement of said first camming member in said first direction.

a control arm connected to said one of said camming members for movingsaid one of said camming members in said second direction,

stop means mounted on said escapement rack, and

abutment means supportedly connected to said frame means incooperatively spaced relationship with respect to said stop meanswhereby the motion of said escapement rack along said axis of rackmovement is limited by engagement of said stop means with said abutmentmeans.

said escapement rack comprises a cylindrical rod,

said first camming member is rotatably carried by said cylindrical rodfor rotational movement in said second direction and said second cammingmember is stationarily secured with respect to said frame means.

1. A typewriter having printing and paper support means definingtherebetween a printing point movable along a writing line, frame means,letter feeding mechanism comprising an escapement rack, means supportingsaid escapement rack on said frame means for movement along an axis thatis parallel to said writing line, wherein the improvement comprises:first and second opposed camming members, connecting means connectingsaid first camming member to said escapement rack for unitary movementtherewith in a first direction that is parallel to said writing line,means connected with said frame means for supporting said second cammingmember against movement in said first direction, one of said cammingmembers being supported for movement relative to the other said cammingmember in a second direction that is transverse to said first direction,said first and second camming members each providing a plurality ofcamming surface portions that are symmetrically spaced about said axisof rack movement and are mutually configured such that relative movementtherebetween in said second direction produces relative movement of saidfirst camming member in said first direction, a control arm connected tosaid one of said camming members for moving said one of said cammingmembers in said second direction, stop means mounted on said escapementrack, and abutment means supportedly connected to said frame means incooperatively spaced relationship with respect to said stop meanswherebY the motion of said escapement rack along said axis of rackmovement is limited by engagement of said stop means with said abutmentmeans, said escapement rack comprises a cylindrical rod, said firstcamming member is rotatably carried by said cylindrical rod forrotational movement in said second direction and said second cammingmember is stationarily secured with respect to said frame means.